A Quasar Pair Sample Compiled from DESI DR1

TL;DR

This paper presents a large, visually classified sample of 1,220 quasar pairs from DESI DR1, providing a valuable resource for studying galaxy mergers, black hole growth, and gravitational lensing.

Contribution

The study compiles and classifies the largest spectroscopically confirmed quasar pair sample to date, including new candidates and lensing systems, enabling more robust statistical analyses.

Findings

Sample contains 1,220 quasar pairs and candidates.

Redshift distribution peaks at 1-2.5, with a weak redshift dependence.

Most pairs show velocity differences indicating dynamical association.

Abstract

Interacting quasar pairs (QPs, either dual or binary) provide crucial insights into galaxy mergers, black hole growth, and large-scale structure formation. The current literature reports fewer than 200 spectroscopically confirmed QPs, highlighting the need for larger samples to enable statistically meaningful investigations. In this paper, we present a sample of 1,220 quasar pairs or candidates compiled from the DESI DR1 quasar sample. Among them, 145 systems have been previously reported. We visually classified the full sample using DESI Legacy Images and SPARCL spectra into three categories: QP (quasar pairs, N = 1020), QPC (quasar pair candidates, N = 142), LQC (lensed quasar candidates, N = 58). Within the LQC subset, we find an intriguing wide-separation ($\sim$7.15$^{\prime\prime}$) quadruply lensed quasar candidate. The redshift distribution of pair sample peaks at $z \sim 1$--$2.5$, with an overall pair fraction of $6.2^{+0.2}_{-0.2}\times10^{-4}$ (Poisson error) and a generally weak redshift dependence. 63.8\% of QPs have $|\Delta V_r| < 600$\,km/s, suggesting dynamical associations. This sample offers a statistically meaningful dataset for future studies of quasar pairs, lensing events, and potentially merger-triggered or merger-induced SMBH growth across the merger sequence.